Process of bleaching animal and vegetable materials



Patented Mar. 20, 1928.

umrao STATES PATENT OFFICE.

man 0. mac, or snow rune, nnw YORK, mrenon m manur nnmomo ooaromnox, aoonrom'rxon or nmwau P100188 Oil BLELOEING ANNA]; AND VlGl'I-APLI lumen.

Io Drawing.

This invention relates tonew and useful improvements in processes ofbleaching animal and vegetab e materials, but 1s designed more speciallfor use in a process for bleaching groun wood pulp, and has for itsprincipal objects:

First, to increase the efiiciency and speed with which such bleaching iscarried out,.

particularly with reference to ground wood ul p S cond, to effect a reatincrease in the degree of activity an effectiveness of the fundamentalbleaching agents operative in the present bleaching processes, by awholly different treatment.

Third, to roduce a bleached ground wood pulp of hig er quality than is'obtamed by present methods.

Further objects, apparent to those skilled in the art, will appear fromthe following description.

The process of the present invention is suitable for use in bleachingsubstances other than ground wood pulp capable of being bleached bysulphurous acid such as, for example, palm leaf, straw, s lk, cane,wool,. etc.

In the following description and clalms, the term animal and-vegetablematerials will be understood to include such substances, the bleachingof ground wood pulp being the preferable application of the lnventlon.

The existing methods of bleachlng ground wood pulp are carried out byapplylng to the pulp, at densities from about 3 0% to 45% bone dry ulp,a solut1on of sodium or calcium bisulp ite and, at times, concentratedsulphuric acid. The pulp, in laps, is allowed to remain in the air forone or two days or longer, for the bleaching to become completed as faras possible, and the bleach-- ing chemicals are applied to the pulp onthe couch roll of the wet press, or similar machine. I

The bleaching is presumably effected by both sulphonation of the colormgmatter of the pulp to form soluble, colorless, coloringmattersulphonates, and also by reduction."

The first reactions are made by the sulphurous acid itself and thesecond, by the nascent hydrogen evolved from the sulphurous 'acid.

The bleaching of ground wood pulp at present is done both with, andwithout, the use of sulphuric acid to speed up the bleach in by rapidevolution 'of free sulphurous acid from the bisulphite.

Application ma se arate: a, 1m. mm Io. 54,510.

These methods have serious disadvan including lrregularities in the aplicatlon of the blsulphite solution, due to inherent short-comm in the euipment used, frequently resu ting in strea ed or incompletely bleachedpulp. I

The s ace required for storin the pul whlle b caching moreover, is lare, an costly, and interferes with other m1 atlons. The bleached pulpretains an, odor of sulphurous acid, due to chemical residues left 1n1t, These residues causetrouble and expense in manufacturing paper fromthe pulp, such as decolorizing of aniline dyes, cp'rosion of equipment,acid in the paper, e

The labor necessary for for the storage period during bleaching, an forunpillng it or use, is considerable. The permanence of the colorobtained is not sufliciently great for man urposes, and the degree ofwhiteness o tainable is often msuflicient. Usually, only new ground woodpul as it 1s belng manufactured, can be bleac ed, as the wet -lpressesor equivalent equipment are ordinari y an integral part of the groundwood pulp manufacturing process. Because of this last condition, theexisting methods do not permit of being efliciently used with the othermethods and equipment of the mill. Lastly, the bleaching is very slow.

A further object of the invention is to avoid the foregoing difficultiesand disadvantages as well as to greatly increase the efiiciency, speedand quality of the bleaching. I have discovered that, if ground woodpulp be circulated in water at densities of from 4% to 40% bone dry pulpand at temperatures of from F. to 200 F., with a mixture of. abisulphite or bisulphites, an acid other'than sulphurous acid, and free1 operpiling the pul washed with water until e of acid and thferundesired materials, the foregoing ob wer are attained, and the pulp isbleached free fr om the above disadvantages and in the most facile,economical and satifacto manner. It may be added that under ordlnaryconditions the temperature above referred to should not be over 165 F.because of the danger of darkening the pulp. There are conditions wheregreater temperatures would not darken the pulp, but they would notusually be met with in practice.

' hydrosulphite, as reducing material.

I have further discovered that if nascent hydro en in larger amountsthan is evolved from 518 amount of sulphurous acid used, be kept incontact with the (pulp while it is being bleached as describe above, thepermanence and whiteness of the bleach is improved and the speed of thebleaching process is considerably increased.'

It should be understood, however, that the practice of my process,without the nas cent hydrogen as described, produces faster bleaching,and a better color and permanence to the bleach than resent methods, dueto the fact that both t e sulphonation and re- "duction are greatlyaccelerated by the conditions of my process.

The details of carrying out my process a dmit of several variations,which will be apparent to those skilled in the art, without departurefrom the spirit of the invention, 'which resides in circulating theground wood pulp with sulphurous acid, and then washing the pulp, so asto remove the acids and other undesirable material therefrom.

The following is given as an illustration of the method of the inventionas applied to ground wood pulp.

Ground wood pulp and water are mixed in the proportions of about 7% bonedry pulp and about 93% water. To each 2,000 pounds of the bone dry pulp,there are added about 115 pounds of sodium bisulphite, 20 or 25 poundsof concentrated sulphuric acid (66 degrees Baum) and 10 pounds of sodiumThese chemicals are preferably dissolved in water. and then added to thepulp." p I The mixture is then circulated for one or two hours within atemperature range of from F. to 200 F., but usually'at a temerature of130-150 degrees Fahrenheit. It 1s then washed withwater until free fromacids and other undesired materials, and the pulp is bleached, cleansedand ready for use.

My invention is not limited to any particular bleaching or washingequipment, as any ap aratus of suitable construction and adapte tocarrying out the process may be.

used. The invention is not limited moreover to any specific means forobtaining the nascent hydrogen in the material being bleached, nor toany particular temperature, density or thickness, or rate ofcirculation.

Nor is the invention limited to, any specific bisulphites, or acid(other than sulphurous) or reducing material. I

The amount of acid, other than sulphurous acid, used, can be variedwithin wide limits depending on speed of bleaching desired, cost limits,etc. It is advisable, however, to use enough sulphuric acid so that anexcess thereof remains when bisulphites of metals whosesulphites areinsoluble in neutral or alkaline solution, are used.

For example, sulphite pulp cooking acid,

which consists of a mixture of calcium bisulphite, ma esium bisulphite,and free sulhurous aci can be used as a source of both isglphites andsome of the free sulphurous aci To furnish the nascent hydrogen anysuitable sources'of nascent hydrogen, such as hydrosulphites, zinc,electrolysis, etc., can be used. In this event, the nascent hydrogen isformed in the presence of the nip.

H drosulphites, to be adde to the ulp, can e conveniently formed frombisulpiiites, such as sulphite ulp cooking acid or sodium bisulphite, byre uction, by zinc dust or foil, and also by electrolysis,

The amount of hydrosulphite used should be small as com ared with theamount of hisulphite, in or er to prevent the formation of freehydrosulphurous acid, which decomposes into sulphur dioxide and finelydivided sulphur, and the presence of the latter may com licate thewashing step.

T e formation of the hydrosulphite may be done either in the bleachingequipment during bleaching or previously, and then added to the mixture.

Temperatures between 80 degrees Fahrenheit and 200 degrees Fahrenheitcan be used under different conditions; and densities or thicknesses offrom 4% bone dry-material to 40% bone dry material. a

What I claim is:

1. The process ofbleachin ground wood pulp, which consists in circuating the pulp 1n water having mixed therewith a bisul' than the sulp,urous acid, and finally washing the mixture with water until free ofacid and other undesired materials.

2. The process of bleach ground wood pulp, which consists in circu atingthe phit'e, free sul hurous acid, and an acid other a in water havingmixed therewith abi phite, free sulphurous acid, an acid other thansulphurous acid, and nascent h drogen in larger amounts than is given 0the amount of sulphurous acid used, and

ally

washing the mixture with water until free of acid and other undesiredmaterials.

3. The process of bleaching ground wood pulp, which consists incirculating the pulp in water, at, densities of from 4% to 40% and attemperatures between 80 F. and I 200 F., with a bisulphite', freesulphurous acid, an acid other than sulphurous acid, and nascenthydrogen in larger amounts than is 'given ofi by the amount ofsulphurous acid used, and then washing the mixture with water until freeof acid and other undesired materials.

4. The process of bleachin ground wood pulp, which consists in circuating the pulp, at densities of form 4% to 40% and at temperaturesbetween 80 F. and. 200 F., in water having mixed therewith a bisulphite,andan acid other than sulphurous Ill acid, and finally washing themixture with water until free of acid and otherundesircd materials.

5. The process of bleaching ground wood pulp, which consists incirculating the pulp in water having mixed therewith sodium bisulphite,concentrated sulphuric acid, and sodium hydrosulphite, and finallywashing the mixture until free from acid and other undesired materials.

6. The process of bleaching ground wood pulp, which consists incirculating the pulp in water and in contact with a bleaching agent atdensities of from 4% to 40% and at tem eratures between 80 F. and 200 R,an then washing-the pulp with water until free of acid and otherundesired materials.

7. The process of bleaching ground wood pulp, which consists incirculating the pulp in water in contact with a bisulphite, free pulp,which consists in circulating the pulp in water, at densities of from 4%to 40%, in contact with a bisulphite, free sulphurous acid, an acidother than sulphurous acid, and nascent hydrogen.

10. The process of bleaching ground wood pulp, which consists incirculatlng the pulp in water, at densities of from 4% to 40% and attemperatures between 80 F. and 200 F., in contact with a bisulphite,free sulphurous acid, and an acid other than sulphurous acid.

11. The process of bleaching ground wood pulp, which consists incirculating the pulp in water, at densities of from 4% to 40% and attemperatures between 80 F. and 200 F., in contact with a bisulphite,free sulphurous acid, an acid other than sulphurous acid, and nascenthydrogen.

12. The process of bleaching ground wood pulp, which consists incirculating the pulp in water, at densities of from 4% to 40% and attemperatures between 80 F. and 200 F., with a bisulphite, freesulphurous acid, an acid other than sulphurous acid, and finally washingthe whole. with water until free from acid and other undesiredmaterials.

In testimony whereof I have afiixed my signature.

ALFRED O. BRAGG.

